Self-crosslinking aqueous polystyrene-butadiene dispersions for consolidating bituminizable nonwovens and also consolidated nonwovens

ABSTRACT

Self-crosslinking aqueous polymer dispersions which are suitable for consolidating nonwovens, which may be subsequently bituminized.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to self-crosslinking aqueouspolymer, e.g., polystyrene-butadiene, dispersions for consolidatingbituminizable base materials such as, for example, bituminized roofingmats and also to the nonwovens consolidated using these polymerdispersions.

[0003] 2. Background of the Invention

[0004] EP-A-0438 284 describes an aqueous polymer emulsion having a lowfree-formaldehyde content, which is achieved by usingN-methylolacrylamide as formaldehyde scavenger. The compound is used forcrosslinking polyvinyl acetate and vinyl acetate-styrene dispersions.

[0005] WO 97/32930 describes an aqueous dispersion for coating textileswhich is composed of a hydrophilic polyurethane (PU) and a copolymer ofstyrene, butadiene and further copolymerizable monomers. These PUdispersions are used for coating roofing mats.

[0006] DE-A 40 29 733 describes bound nonwovens comprising a bindercomposed of a dispersion prepared by polymerization of a conjugateddiene, and α,β-unsaturated mono- or dicarboxylic acid and hydroxylcontaining olefinic monomers.

[0007] U.S. Pat. No. 4,125,663 discloses a process for the production ofbound nonwovens using a polymer dispersion comprisingmelamine/formaldehyde resins as crosslinkers.

[0008] Bituminized roofing mats are produced by saturating and/orcoating a base material with bitumen. The formerly used base materialscomposed of cardboard failed to keep pace with increasing performanceexpectations and have been superseded by raw felt, woven jute fabric,glass mats, mixed glass fiber cloth and especially by polyesterspunbondeds and also polyester staple fiber webs. Such nonwovens,consolidated with dispersion binder, for example, have to meet thefollowing performance requirements in bituminization and end use:

[0009] Low Extensibility at 160 to 200° C. Under High Tensile Stress,High Mechanical Strength

[0010] The reinforcing construction of bound nonwoven should extendlittle if at all under the production conditions of bitumen impregnationand/or coating. 1% extension must not be exceeded at 160 to 200° C. andthe high tensile stresses due to the highly viscous bitumen and the highproduction speeds. A higher extensibility would cause stresses to befrozen into the roofing mat as it cooled down and was wound up, whichwould become rereleased on renewed heating, for example in the course ofthe welding of the seams or in the event of strong insolation. Thiswould lead to cracks in the roof membrane. The low-extensibilityrequirement applies longitudinally, transversely and diagonally.

[0011] Good Adhesion to Bitumen

[0012] Low Sensitivity to Water, High Watertightness

[0013] If the bound nonwovens (fiber material, binder) are notsufficiently hydrophobic, the wicking effect of individual filaments maycause water to ingress at the points of intersection of the roofingmats. This leads to separation between the bitumen and the boundnonwoven or to frost damage.

[0014] Flexibility and Extensibility of Construction in End Use

[0015] Owing to temperature fluctuations in end use (−40° C. to +80° C.)and differences in the expansion coefficients of various buildingmaterials, the entire roofing mat is subject to relatively largedimensional changes. Excessive stiffness and inflexibility of theoverall construction gives rise to fine cracks which, combined withmoisture and low temperatures, lead to the destruction of the roofingmat. It is therefore urgently necessary that not only the bitumen butalso the reinforcement of bound nonwoven remain flexible at the usetemperature.

SUMMARY OF THE INVENTION

[0016] The present invention is based on the surprising discovery thatpolymers of aromatic vinyl compounds and conjugated dienes, e.g.,styrene-butadienes, copolymerized with compounds havingself-crosslinking groups are useful for impregnating nonwovens. The endproducts obtained have the required dimensional stability at hightemperatures and are substantially insensitive to water. Roomtemperature mechanical properties are similar to those of standardsystems.

[0017] Accordingly, the present invention provides self-crosslinkingaqueous polymer dispersions for consolidating bituminizable nonwovens,composed of the following polymerized monomer units:

[0018] 1) 20 to 55 parts, based on the dry mass of the disperse phase,of at least one conjugated diene,

[0019] 2) 30 to 80 parts, based on the dry mass of the disperse phase,of at least one copolymerizable aromatic vinyl compound,

[0020] 3) 0.1 to 10 parts, based on the dry mass of the disperse phase,of at least one polymerizable organic carboxylic acid and/or anhydride,

[0021] 4) 1 to 10 parts of at least one crosslinker,

[0022] 5) 0 to 20 parts, based on the dry mass of the disperse phase, ofat least one derivative of an α,β-unsaturated carboxylic acid.

[0023] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription.

DETAILED DESCRIPTION OF THE INVENTION

[0024] A particularly useful component 1) is 1,3-butadiene. Other1,3-dienes may be used as well, for example isoprene, chloroisoprene or2,3-dimethylbutadiene. Butadiene is preferred.

[0025] The preferred component 2) is styrene. Other aromatic vinyls maylikewise be used, for example methylstyrene or styrene carboxylic acids.

[0026] Useful copolymerizable organic carboxylic acids (component 3)include, for example, acrylic acid, methacrylic acid or itaconic acid,used alone or mixed. Maleic acid, fumaric acid, maleic anhydride andfumaric anhydride may also be used. Acrylic acid and/or methacrylic acidare preferred.

[0027] The crosslinker (component 4) is in principle an acrylamide or amethacrylamide. The following compounds are preferred:N-methylolacrylamide, N-methoxymethylacrylamide,N-hydroxymethylacrylamide, N-methylolmethacrylamide,N-methoxymethylmethacrylamide and N-hydroxymethylmethacrylamide.

[0028] Useful derivatives of α,β-unsaturated carboxylic acids (component5) include the following compounds: acrylamide, methacrylamide,acrylonitrile and methacrylonitrile.

[0029] It is further possible to use the hereinbelow described mixturesof self crosslinking dispersions for consolidating bituminizablenonwovens.

[0030] By blending “soft” and “hard” types it is thus possible to freelyselect different nonwoven application properties, e.g., pliability.

[0031] A hard styrene-butadiene rubber (SBR) type, for example, has thefollowing composition: 60% of styrene, 28% of butadiene, 8% ofacrylonitrile, 2% of acid, 4% of crosslinker; a soft SBR type, forexample, has the following composition: 35% of styrene, 42% ofbutadiene, 10% of acrylonitrile, 7% of acrylamide, 2% of acid, 4% ofcrosslinker.

[0032] In general, mixing ratios for soft component: hard component arechosen between 7:3 and 0:10.

[0033] Preference is given to mixtures between the soft component: hardcomponent mixing ratios of 5:5 to 1:9, particularly 3:7 to 2:8.

[0034] The inventive dispersions for consolidating nonwovens may alsocomprise auxiliary and additive substances, for example anionicemulsifiers, nonionic emulsifiers, aging inhibitors, biocides,defoamers, pH buffers, and complexing agents.

[0035] The present invention also provides consolidated nonwovensconsolidated using a self-crosslinking aqueous polymer dispersion,composed of the following polymerized monomer units:

[0036] 1) 20 to 55 parts, based on the dry mass of the disperse phase,of at least one conjugated diene,

[0037] 2) 30 to 80 parts, based on the dry mass of the disperse phase,of at least one copolymerizable aromatic vinyl compound,

[0038] 3) 0.1 to 10 parts, based on the dry mass of the disperse phase,of at least one polymerizable organic carboxylic acid and/or anhydride,

[0039] 4) 1 to 10 parts of at least one crosslinker,

[0040] 5) 0 to 20 parts, based on the dry mass of the disperse phase, ofat least one derivative of an α,β-unsaturated carboxylic acid.

[0041] Nonwovens that may be used in the present invention include allknown nonwovens, for example nonwovens composed of glass, polymers andnatural products and also their hybrid constructions, especially fromraw felt, woven jute fabric, glass mat, mixed glass fiber cloth,polyamide and polyester. Spunbonded nonwovens and staple fiber nonwovensare preferred. Polyester spunbondeds and polyester staple fiber webs areparticularly preferred. The nonwovens used are readied for this use in aconventional manner, i.e. needled or heat-set. The nonwovens generallyhave a weight of 20-350 g/m², preferably 100-250 g/m².

[0042] The components 1) to 5) and further, auxiliary and additivesubstances are present as described above.

EXAMPLES

[0043] Having generally described this invention, a furtherunderstanding can be obtained by reference to certain specific exampleswhich are provided herein for purposes of illustration only and are notintended to be limiting unless otherwise specified.

[0044] The examples which follow illustrate the invention: MonomerInventive Ex. 1 Inventive Ex. 2 1,3-Butadiene 32 parts 40 parts Styrene62 parts 37 parts Acrylonitrile  0 parts 10 parts Acrylamide  2 parts  7parts Acid  2 parts  2 parts Crosslinker  2 parts  4 parts

[0045] The other starting materials important for the emulsionpolymerization, e.g. initiators, emulsifiers, molecular weightregulators and aging inhibitors, are used in the production process inthe prior art types and amounts. The same applies to the polymerizationprocess used for the production.

[0046] Illustrative Production Process

[0047] A polymerization tank is charged with completely ion-free water,the customary emulsifiers and auxiliaries and the monomers.

[0048] The batch is heated to about 50° C., at which point thefree-radical former is added. The temperature is raised (about 90° C.)and the polymerization is completed in the course of 6-8 h. Acoagulum-free dispersion is obtained.

[0049] The details of the production process are described in Examples 1to 9 and A to F of DE-A 38 40 512 (Hüls AG), on pages 5 to 7.

[0050] The solids content was determined according to DIN 53 189.

[0051] The following dispersions were characterized with regard to theirapplication properties: Solids Viscosity Glass transition contentBrookfield temperature Dispersion [%] [mPas] pH [° C.] Comparative Ex. 150 100 4.5 30 standard (styrene-acrylate) Comparative Ex. 2 50 150 2.549 standard (straight-acrylate) Comparative Ex. 3 50 <100  8.5 44 (Inv.Ex. 1 without self- crosslinking group) Inventive Ex. 1 (self- 50  904.5 41 crosslinking SBR) Inventive Ex. 2 (self- 40  25 8.0 25crosslinking SBR)

[0052] Mixtures of the self-crosslinking SBR types were included in thetests as well. By blending “soft” and “hard” types it is thus possibleto freely select different nonwoven application properties (e.g.pliability).

[0053] Determination of Dimensional Stability

[0054] The determination was carried out according to DIN 18192 (point5.7). For characterization, a spunbonded web is foam-impregnated on aMathis pad-mangle (nip: -10) with the following liquor: Aqueousdispersion (50% strength):   250 g Rohagit SL 215:  7.5 g (foamingagent) Rohagal 10 n:  1.0 g (foam stabilizer) Completely ion-free water:241.5 g

[0055] Prior to impregnation the web is preshrunk at 220° C. for 5 min.After impregnation, it is dried and cured at 180° C. for 10 min. Thehereinbelow recited results are averages of three individualdeterminations in each case.

[0056] Rohagit SL 215 is a foaming agent which is commercially availablefrom Röhm GmbH. This material is an aqueous solution of an acrylicpolymer.

[0057] Rohagal 10 n is a foam stabilizer which is commercially availablefrom Röhm GmbH. This material is a nonionic surfactant based on fattyalcohol polyalkyl ether. Binder Dimensional Dimensional add-on changechange Dispersion [%] MD [%] XD [%] Comparative Ex. 1 24.5 1.25 1.0Comparative Ex. 2 24.0 1.25 1.25 Comparative Ex. 3 25.5 15 17 InventiveEx. 1 24.0 1.0 1.0 Inventive Ex. 2 23.5 0.75 1.0 Inventive Ex. 3 (1:1mixture of 24.0 1.0 1.0 Inventive Examples 1 and 2)

[0058] The nonwovens produced using the dispersions of the inventionexhibit distinctly less shrinkage.

[0059] Spunbondeds impregnated with Inventive Example 1 and InventiveExample 2 or a mixture of the two have a dimensional stability which issimilar or in some instances superior to that of standard systems. Theseproducts comply with the limit values stipulated in the DINprescription. An SBR without self-crosslinking groups does not providean acceptable DIN 18192 performance. Such a system cannot be used as anonwoven.

[0060] It is known in the field that addition of melamine-formaldehyde(MF) resins or of similar compounds may improve an inadequatedimensional stability. As the following table shows, this is alsopossible in the case of Comparative Example 3. However, the stipulatedvalues and the results of Inventive Example 1 or Inventive Example 2 arenot achieved, however. Binder Dimensional Dimensional add-on changechange Dispersion [%] MD [%] XD [%] Comparative Ex. 3 25.5 15 17Comparative Ex. 4 24.0 3.0 2.5 (Comparative Ex. 3 + 10% MF (solid onsolid))

[0061] An example of a useful melamine-formaldehyde is Cassurit MT (fromClariant).

[0062] Determination of Capillary Rise

[0063] To test the sensitivity to water and the capillarity, 3 cm widestrips of the bound and dried nonwovens are dipped vertically into awaterbath, to a depth of one centimeter. The water is then free to risevertically in the bound nonwoven. The rise over 24 hours is determinedin centimeters. Binder add-on Capillary rise Dispersion [%] [cm]Comparative Ex. 1 24.5 <1 Comparative Ex. 2 24.0 <1 Comparative Ex. 325.5 0 Inventive Ex. 1 24.0 <1 Inventive Ex. 2 23.5 <1 Inventive Ex. 324.0 1.0

[0064] Determination of Breaking Strength of Bound Nonwovens at RT

[0065] The test is carried out on the lines of DIN EN ISO 527-1 and DINEN ISO 527-3. Samples 15 cm long and 5 cm wide are cut out of the boundnonwovens, conditioned for 24 hours at 23° C. and 50% relative humidityand then characterized on an Instron tensile tester.

[0066] The test parameters used were as follows: Strain rate: 100 mm/minNonwoven thickness:  2 mm Measuring range:  0-5000 N Clamped length:  50mm

[0067] The results are shown hereinbelow: Comp. Ex. 1 (SA) Inv. Ex. 1Inv. Ex. 3 Extension Force [N] Force [N] Force [N]  2% 126 165 115  3%190 230 185  5% 262 310 256 10% 354 398 340 15% 424 458 400 Force (max)803 744 701 Extension (max)  60%  53%  58%

[0068] Thermal Stability

[0069] Since, as described above, the bound nonwovens are processed in ahot bitumen bath at 200° C., the change in the mechanical properties onexposure to thermal stress is of interest. Since the styrene-butadienepolymers, unlike styrene-acrylates and straight acrylates, still containreactive double bonds after polymerization which are capable of reactingwith a wide range of partners, for example free radicals (atmosphericoxygen), at high temperatures, the changed binder properties afterexposure to thermal stress deserves particular attention.

[0070] The bound nonwovens were heat-treated at 200° C. for 30 min andthen assessed. Compared with the standard styrene-acrylate and straightacrylate systems, the nonwovens which have been finished with SBR are insome cases badly browned. Since, however, the nonwoven is surfaced bytwo bitumen layers (top and bottom) in end use and thus not directlyvisible, this purely visual defect is not relevant for the contemplateduse segment. A test of the mechanical properties (dimensional stability)after the heat treatment did not produce inferior results.

[0071] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

[0072] This application is based on German Patent Application Ser. No.10000446-6, filed on Jan. 7, 2000, and incorporated herein by referencein its entirety.

1. A self-crosslinking aqueous polymer dispersion suitable forconsolidating bituminizable nonwovens, comprising the followingpolymerized monomer units: 1) 20 to 55 parts, based on the dry mass ofthe disperse phase, of at least one conjugated diene, 2) 30 to 80 parts,based on the dry mass of the disperse phase, of at least onecopolymerizable aromatic vinyl compound, 3) 0.1 to 10 parts, based onthe dry mass of the disperse phase, of at least one polymerizableorganic carboxylic acid and/or anhydride, 4) 1 to 10 parts of at leastone crosslinker, 5) 0 to 20 parts, based on the dry mass of the dispersephase, of at least one derivative of an α,β-unsaturated carboxylic acid2. The dispersion of claim 1 , wherein 1) comprises at least one monomerunit selected from the group of monomers consisting of 1,3-butadiene,isoprene, chloroisoprene and 2,3-dimethylbutadiene.
 3. The dispersion ofclaim 1 , wherein 2) comprises at least one monomer unit selected fromthe group of monomers consisting of styrene, methylstyrene and styrenecarboxylic acid.
 4. The dispersion of claim 1 , wherein 3) in thedispersion comprises at least one monomer unit selected from the groupconsisting of acrylic acid, methacrylic acid, itaconic acid, maleic acidand fumaric acid.
 5. The dispersion of claim 1 , wherein 4) comprises atleast one monomer selected from the group consisting ofN-methylolacrylamide, N-methoxymethylacrylamide,N-hydroxymethylacrylamide, N-methylolmethacrylamide,N-methoxymethylmethacrylamide and N-hydroxymethylmethacrylamide.
 6. Thedispersion of claim 1 , wherein 5) comprises at least one monomerselected from the group consisting of acrylamide, methacrylamide,acrylonitrile and methacrylonitrile.
 7. The dispersion of claim 1 ,wherein 1) comprises 1,3-butadiene and 2) comprises styrene.
 8. Aconsolidated nonwoven consolidated using a self-crosslinking aqueouspolymer dispersion, composed of the following monomer components: 1) 20to 55 parts, based on the dry mass of the disperse phase, of at leastone conjugated diene, 2) 30 to 80 parts, based on the dry mass of thedisperse phase, of at least one copolymerizable aromatic vinyl compound,3) 0.1 to 10 parts, based on the dry mass of the disperse phase, of atleast one polymerizable organic carboxylic acid and/or anhydride, 4) 1to 10 parts of at least one crosslinker, 5) 0 to 20 parts, based on thedry mass of the disperse phase, of at least one derivative of anα,β-unsaturated carboxylic acid.
 9. The consolidated nonwoven of claim 8, wherein 1) in comprises at least one monomer selected from the groupof monomers consisting of 1,3-butadiene, isoprene, chloroisoprene and2,3-dimethylbutadiene.
 10. The consolidated nonwoven of claim 8 ,wherein 2) comprises at least one monomer selected from the groupconsisting of styrene, methylstyrene and styrene carboxylic acid. 11.The consolidated nonwoven of claim 8 , wherein 3) comprises at least onemonomer unit selected from the group consisting of acrylic acid,methacrylic acid, itaconic acid, maleic acid and fumaric acid.
 12. Theconsolidated nonwoven of claim 8 , wherein 4) comprises at least onemonomer unit selected from the group consisting of N -methylolacrylamide, N-methoxymethyl acrylamide, N-hydroxymethylacrylamide,N-methylolmethacrylamide, N-methoxymethylmethacrylamide andN-hydroxymethylmethacrylamide.
 13. The consolidated nonwoven of claim 8, wherein 5) comprises at least one monomer unit selected from the groupconsisting of acrylamide, methacrylamide, acrylonitrile andmethacrylonitrile.
 14. The consolidated nonwoven of claim 8 , whereinthe nonwovens used are composed of glass, polymers and natural productsand also their hybrid constructions, especially from raw felt, wovenjute fabric, glass mat, mixed glass fiber cloth and polyester.
 15. Theconsolidated nonwoven of claim 14 , wherein the nonwovens used arepolyester spunbondeds or polyester staple fiber webs.
 16. A method ofproducing the consolidated nonwoven of claim 8 , comprising impregnatingthe nonwoven with said aqueous polymer dispersion followed by curing thepolymer.
 17. A method of producing aqueous polymer dispersion of claim 1comprising polymerizing the following monomers in water: 1) 20 to 55parts, based on the dry mass of the disperse phase, of at least oneconjugated diene, 2) 30 to 80 parts, based on the dry mass of thedisperse phase, of at least one copolymerizable aromatic vinyl compound,3) 0.1 to 10 parts, based on the dry mass of the disperse phase, of atleast one polymerizable organic carboxylic acid and/or anhydride, 4) 1to 10 parts of at least one crosslinker, 5) 0 to 20 parts, based on thedry mass of the disperse phase, of at least one derivative of anα,β-unsaturated carboxylic acid